This invention relates to a control apparatus for controlling a light source and, more particularly, to a control apparatus for controlling a luminous energy of the light source in an image input apparatus.
In general, an image input apparatus is provided with a cold-cathode tube light source (CCFL) and a read-in solid imaging device (CCD). In the image input apparatus, the CCFL irradiates a light to a document paper in order to read the image from the document paper by the CCD. On reading the image from the document paper by the CCD, it is necessary to properly control a luminous energy of the CCFL.
When the CCFL is put into an on-state in a conventional image input apparatus, the luminous energy reaches a predetermined energy in the CCFL after a predetermined time lapses. After the luminous energy reaches the predetermined energy in the CCFL, the conventional image input apparatus starts to read the image from the document paper by the CCD to obtain the image. More particularly, a time duration lapse needs until the luminous energy reaches the predetermined energy in the CCFL after the CCFL is put into an on-state. The time duration lapse will be called a rise time. The rise time is determined on the basis of a characteristic of CCFL. As described above, the conventional image input apparatus starts to read the image from the document paper by the CCD after the luminous energy is stabilized.
As described above, it is necessary to start to read the image from the document paper in the conventional image input apparatus after the luminous energy is stabilized in CCFL. In other words, it is impossible to start to read the image from the document paper in the conventional image input apparatus until the luminous energy is stabilized in CCFL. As a result, a user must wait to read the image from the document paper after the luminous energy is stabilized in CCFL.
In order to read the image from the document paper at once after the CCFL is put into the on-state, an environmental temperature of the CCFL may be kept at a predetermined temperature. More particularly, the environmental temperature of the CCFL is controlled to the predetermined temperature by a heater system. However, a waiting or stand-by consumption power increases when the environmental temperature of the CCFL is controlled to the predetermined temperature by the heater system.
Furthermore, a fluorescent tube may be used as the light source instead of the CCFL. The fluorescent tube is constituted by only an inert gas and does not contain mercury or the like having a high dependency on a tube temperature. When the fluorescent tube is used as the light source instead of the CCFL, it is difficult to obtain a sufficient luminous energy although a rise time characteristic is improved.